The present invention relates to a system for controlling the ignition timing of an internal combustion engine such as an automotive engine.
Japanese Patent Laid Open No. 61-157771 (U.S. Pat. No. 4,620,518) discloses a control system wherein the operation thereof is divided into a rough correction and a fine correction. In the rough correction, a coefficient for correcting a basic ignition timing is obtained so as to approximate the basic ignition timing to a desired ignition timing. In the fine correction, a correcting quantity of the ignition timing is obtained by learning operation in dependence on engine speed and intake air pressure. Thus, the basic ignition timing is further corrected by the correcting quantity. When the correcting quantity in the fine correction exceeds a predetermined limit value, the operation returns to the rough correction, thereby correcting the coefficient to approximate the basic injection timing to the desired timing.
However, the correcting coefficient is corrected only when the motor vehicle is driven under a predetermined driving condition for the rough correction. Therefore, while the vehicle is driven out of the driving condition range, the correcting coefficient cannot be determined so that the rough correction routine is not completed. Accordingly, if a knocking occurs under such a condition, the control system does not operate to prevent the knocking.
Additionally, when the rough correction does not proceed because the vehicle is not driven at a condition for rough correction, for example, at continuous uphill driving, or because the correcting coefficient returns to an initial value owing to disturbances such as noise, the operation does not proceed to the fine correction. Thus, the ignition timing cannot be corrected to stop the knocking.